Site Selectivity for the Spin States and Spin Crossover in Undecanuclear Heterometallic Cyanido-Bridged Clusters

Polynuclear molecular clusters offer an opportunity to design new hierarchical switchable materials with collective properties, based on variation of the chemical composition, size, shapes, and overall building blocks organization. In this study, we rationally designed and constructed an unprecedented series of cyanido-bridged nanoclusters realizing new undecanuclear topology: FeII[FeII(bzbpen)]6[WV(CN)8]2[WIV(CN)8]2·18MeOH (1), NaI[CoII(bzbpen)]6[WV(CN)8]3[WIV(CN)8]·28MeOH (2), NaI[NiII(bzbpen)]6[WV(CN)8]3[WIV(CN)8]·27MeOH (3), and CoII[CoII(R/S-pabh)2]6[WV(CN)8]2[WIV(CN)8]2·26MeOH [4R and 4S; bzbpen = N1,N2-dibenzyl-N1,N2-bis(pyridin-2-ylmethyl)ethane-1,2-diamine; R/S-pabh = (R/S)-N-(1-naphthyl)-1-(pyridin-2-yl)methanimine], of size up to 11 nm3, ca. 2.0 × 2.2 × 2.5 nm (1–3) and ca. 1.4 × 2.5 × 2.5 nm (4). 1, 2, and 4 exhibit site selectivity for the spin states and spin transition related to the structural speciation based on subtle exogenous and endogenous effects imposed on similar but distinguishable 3d metal-ion-coordination moieties. 1 exhibits a mid-temperature-range spin-crossover (SCO) behavior that is more advanced than the previously reported SCO clusters based on octacyanidometallates and an onset of SCO behavior close to room temperature. The latter feature is also present in 2 and 4, which suggests the emergence of CoII-centered SCO not observed in previous bimetallic cyanido-bridged CoII–WV/IV systems. In addition, reversible switching of the SCO behavior in 1 via a single-crystal-to-single-crystal transformation during desolvation was also documented.

. Crystal data and structure refinement of 1 and 1 de at different temperatures ..... 22 Table S2. Crystal data and structure refinement of 2 and 3 at different temperatures. ....... 23 Table S3. Crystal data and structure refinement of 4S and 4R at different temperatures. .. 24 Table S4. Results     .09 g mol -1 ) by SC-XRD experiment performed on crystals protected by Apiezon N grease. Phase purity was proved by powder XRD data (see Figure S7). IR (cm -1 ). weight loss is 3.43%), corresponding to remove 5 methanol molecules (see Figure S14).  To prevent the decomposition of the investigated material in the solid state by spectroscopic techniques the most of further physical measurements were further performed on the crystals placed in the mother liquid (1-4@MeOH), or dispersed in paraffin oil and Apiezon N grease. Powder X-ray diffraction patterns for 1-4@MeOH sealed in glass capillary (0.5 mm) were collected on a PANalytical X'Pert PRO MPD S8 diffractometer with Debye-Scherrer geometry using CuKα radiation (λ = 1.54187 Å; 2θ range: 3-50˚ for RT). The IR spectra were collected using a Nicolet iN10 MX FT-IR microscope in transmission. Measurements were performed on small single crystals covered by paraffin oil in order to avoid desolvation. The UV-vis-NIR spectra were collected on a JASCO V-670 spectrometer for samples 1-4 suspended in paraffin oil, and spread between two glass rollers. 1 de was measured using BaSO4 pellets as the reference background. Natural circular dichroism (NCD) spectra for 4R and 4S (dispersed in Nujol with mother solution, 5-10 mg per several drops, and introduced between CaF2 plates) were collected using a Jasco J-810 spectropolarimeter. The recorded signals were corrected using the blank Nujol signal. The transmission 57 Fe Mössbauer spectra were collected in 1024 channels, with a 10 mCi 57 Co source in an Rh matrix, using a Wissel spectrometer with a bath liquid nitrogen cryostat for selected temperatures in the range between 250 and 80 K. The temperature stabilization was better than 0.5 K. The RT measurements were performed also with the use of the Wissel spectrometer, but without cryostat, with the temperature stabilization +/-2K. The velocity scale was calibrated using the α-Fe foil standard. The ground sample of 1 with a tiny amount of the mother liquor was mixed with Apiezon N grease, whereas 1de was prepared as a powder pellet. Both samples were sealed by Kapton foils in copper rings.
Due to the small resonant effect in the studied complexes, a background contribution to the spectra from iron impurities of the beryllium windows of the cryostat system was precisely measured in a dummy run and was included as a fixed parameter in the fitting procedure. The background spectra of the sample holders did not reveal any significant contribution to the main spectra. Mössbauer spectra were fitted with the use of the WinNormos-for-Igor software package, assuming the Lorentzian shape of the resonance lines, i.e. the saturation effects were not included. Two types of quadrupole doublets were considered in the fits, assigned to the LS Fe II and HS Fe II , respectively. The contribution of the HS states may consist of more components, indistinguishable within measured spectra due to their low intensities. The relative fractions of the HS versus LS states were determined from the ratio of the areas of the corresponding doublets, which means that the equal recoil-free fractions of iron in both spin states were assumed.
Magnetic susceptibility measurements were probed with Quantum Design MPMS 3 S9 SQUID magnetometer. Freshly prepared 1-4 microcrystalline samples were sealed with a small amount of mother liquor in a glass tube to prevent lost solvent, whereas sample of 1 de placed in a foil bag, which was immediately sealed after desolvation. The dc magnetic susceptibilities were measured using the thermal cyclic course 300 K → LT Intensities of reflections for the sample absorption were corrected using multi-scan method. Structures were solved by intrinsic phasing method and refined anisotropically with weighted full-matrix least squares on F 2 using SHELXT 6 and SHELXL 7 programs with Olex 2 graphic interface. 8 For 1 and 1 de , all non-hydrogen atoms were refined anisotropically with restraints (DFIX, ISOR, SIMU and DELU) on methanol molecules and partially phenyl groups.
Hydrogen atoms within structures were placed in idealized positions and refined using riding coordinate model. While methanol molecules in 4R and 4S were refined isotropically. A solvent mask procedure was further performed on 2 and 3 dues to highly disordered interstitial solvent molecules. Crystal data and structure refinement parameters are summarized in Table S1  Wavenumber / cm -1

Composition and general remarks section
Absorbance / a.u.       The observed weight loss of 6.12% is slightly smaller than 6.75% expected for 2 MeOH molecule and 17 H2O in dry residues. This difference is probably due to some weight loss preceding the measurements in RT.          Table S5 and        These contacts parameters are summarized in Table S8.       Table S14. Transition completeness of 1 and 1 de obtained from SC-XRD, magnetic and Mössbauer spectra measurements.   Table   S1). This might be correlated with the increased overall degree of freedom along the c direction as a consequence of the removal of MeOH molecules, all located in the channels running along this direction, and one of them present in the space between the vertex regions of clusters (compare Figure 2 and Figure S25). The representative overlays of the high spin and low spin structures of 1 and 1 de also exhibit the elongated or compressed CN-Fe linkages at the Fe1 sites along this direction ( Figure S33). The large deviation shown by Fe1 at 100 K for Fe1 is due to the fact Fe1 is in a mixed spin state population at this temperature.